The BBC's Virginia Gidley-Kitchin tries to piece together the story behind the alleged involvement of mercenaries in a coup plot in Equatorial Guinea.

The West African state of Equatorial Guinea has been awash for weeks now with rumours of trouble brewing.

President Obiang says "enemy powers" are trying to overthrow him

But events seem to have come to a head.

On Sunday, the authorities in Zimbabwe impounded a plane which flew in from South Africa with 64 alleged mercenaries on board.

What exactly they were up to wasn't clear - particularly as they didn't have any actual weapons with them.

Plot

But on Tuesday, Information Minister August Nse Nfamu claimed that 15 more mercenaries had been arrested in his country and that they were an advance party for the group detained in Zimbabwe.

He said their aim was to overthrow and kill Equatorial Guinea's President Teodoro Obiang Nguema.

The president then went further, declaring that the alleged coup plot had been funded by what he called enemy powers and multinational companies.

Then in a BBC interview, Justice Minister Ruben Mangue, pointed the finger specifically at a leading exiled politician, Severo Moto, head of the opposition Progress Party.

For its part, the Progress Party denied involvement in any such plot.

Mr Moto said the president was just trying to damage his reputation.

"I have absolutely nothing to do with this story. I believe that once again in the face of my announcement of my return to Equatorial Guinea, President Obiang has become nervous and of course he has no trouble plotting and preparing traps like this in order to tarnish my political career and really keep the population on tenterhooks".

Old tricks?

It is not the first time that the government of Equatorial Guinea has alleged its political opponents were plotting to overthrow it.

The benefits of oil have been slow to trickle down

Such allegations have sometimes coincided with the run-up to elections and led to the arrest of opposition politicians - and another opposition leader, Bakale Celestino, claims that, with local elections coming up in April, the government is up to its old tricks again.

But some Equatorial Guinea-watchers think that this time the rumours may be correct.

Patrick Smith, the editor of Africa Confidential magazine, says there isn't any evidence, but military sources in South Africa "are absolutely categorical that the South African soldiers on that plane to Zimbabwe on Sunday were involved in the Equatorial Guinea adventure".

He says they also claim that Severo Moto had a series of discussions with the Spanish Prime Minister Aznar, with a view to getting recognition, were he to succeed in overthrowing the Obiang government.

Patrick Smith says that in recent months, there's been a lot of unease within the Equatorial Guinean military, particularly over the succession issue.

"It is felt that President Obiang's health is not good, and that should he die precipitously, there would be a bloody struggle to succeed him. And one of the key characters likely to lead that struggle would be his son, Teodorin, who is heartily disliked by many other people in the Equatorial Guinea military.

Explosive mix

Justice Minister Ruben Mangue says that rumours of a power struggle are commonplace everywhere but - he insists - completely untrue.

The plane was heading to Equatorial Guinea, the government believes

"The president has just been elected last year for seven years. The president is healthy... it is not serious to talk about the succession to the president now".

It may be too early to know where the truth lies. But Anthony Goldman, Africa analyst for Clearwater Research Services, says that the sudden arrival of oil wealth in what until a few years ago was one of the poorest countries in the world has "created an explosive mix" in Equatorial Guinea.

"It's had an unfortunate passage of dictatorships from the colonial period and then after independence - regimes of unparalleled brutality even in Africa.

"In the 1970s a third of the population were killed or fled into exile under the regime of Masias Nguema. His nephew seized power in 1979, promising to liberalise the country.

"And although now in theory it's a multi-party democracy, opposition supporters, diplomats and a number of human rights activists maintain that it remains a dictatorial regime, fuelled now by the arrival of oil," he says.

It may be no coincidence that, again according to Anthony Goldman, Equatorial Guinea has long had the image of being the kind of small, sleepy place where a handful of mercenaries could quickly seize power.